Various kinds of low storage temperatures such as the temperatures of refrigeration, cold storage, chilled storage, and freezing point storage are used in the logistics of commercial products such as pharmaceutical products and foods. If a temperature deviates from an appropriate management temperature while such a product is transported or stored, the arising problems are: the deterioration of drug efficiency in the case of a pharmaceutical product; and the deterioration of flavor or degeneration such as putrefaction or the like in the case of a food. The present invention relates to a thermochromic display device that develops an irreversible change when it is exposed to a prescribed temperature and can display a temperature history.
In order to solve the above problems, a thermochromic marking (temperature traceable indicator) generating irreversible change when it reaches a temperature not lower than a preset temperature is studied. Although the indicator does not develop a color as long as the storage temperature of a commercial product is lower than a preset temperature, the indicator develops a color at a temperature not lower than the preset temperature and the color does not disappear even when it is cooled again. As a result, the history showing that the temperature of a commercial product has exceeded a preset temperature remains and the history cannot be falsified. Problems in the temperature management of a commercial product can be clarified by collating the history with the degeneration of the commercial product and the like.
As such a marking, a thermochromic marking in which, when a temperature not lower than a certain temperature is reached, a color developing layer melts, touches a color former layer, and irreversibly develops a color is described in Patent Literature 1.